1. Field of the Invention
The present invention relates to transversely excited lasers with either external or internal capacitance coupling and more particularly to an improved matching network which operates efficiently in both the ignition state and steady state.
2. Description of the Prior Art
U.S. Pat. No. 4,352,188, entitled RF Pumped Waveguide Laser with Inductive Loading for Enhancing Discharge Uniformity, issued to Glen A. Griffith on Sept. 28, 1982, teaches a discharge-excited waveguide gas laser which utilizes a transverse rf excitation voltage at a frequency of at least about 30 MHz applied between elongated electrodes on opposite sides of the laser discharge chamber and which utilizes a plurality of shunt inductances coupled between the electrodes externally along the length of the chamber. These inductances provide a negative admittance which compensates for the variation in the phase angle of the transmission line reflection coefficient along the length of the laser discharge chamber. The variation in the magnitude of the standing wave voltage is reduced accordingly thereby improving the uniformity of the laser-exciting discharge.
U. S. Pat. No. 4,169,251, teaches Waveguide Gas Laser with High Freqency Transverse Discharge Excitation, issued to Katherine D. Laakman on Sept. 25, 1979, teaches waveguide lasers which are excited by means of a transverse discharge at rf frequencies generally in the vhf-uhf range, i.e., from about 30 MHz to about 3 GHz. These excitation frequencies are sufficiently high to ensure negligible interaction of discharge electrons with the discharge-establishing electrodes, thereby achieving superior discharge properties which result in a laser of improved performance and reduced size and complexity.
Recently there has been considerable interest in waveguide gas lasers wherein the laser light propagates through a hollow waveguide which also serves to confine the laser-exciting discharge. U.S. Pat. No. 3,772,611, entitled Waveguide Gas Laser Devices, issued to Peter William Smith on Nov. 13, 1973, teaches the basic excitation scheme which was used in most of the early waveguide lasers and which involves establishing a dc electric discharge longitudinally through the device between a pair of electrodes disposed near the respective ends of the laser waveguide. This type of discharge required relatively large dc excitation voltages of around 10 Kv along with the necessary power supply and associated circuitry for generating voltages of this magnitude.
U.S. Pat. No. 3,772,611, also teaches the exciting of a ring-type waveguide laser from an rf source by means of a coil wound around the ring-shaped waveguide. Such a coil-type excitation arrangement not only is incapable of providing a highly uniform discharge, but it also affords poor coupling efficiency. Moreover, when more than a few coil turns are employed, the inductance of the coil becomes sufficiently large to limit the usable excitation frequencies below a few MHz.
In order to obtain a more uniform discharge with reduced excitation voltage, waveguide lasers have been developed wherein a pulsed discharge is established along a transverse waveguide dimension. U.S. Pat. No. 3,815,047, entitled Transversely-Excited Waveguide Gas Laser, issued to Peter William Smith and Obert Reeves Wood on June 4, 1974, teaches transversely-excited waveguide gas lasers which include a structure having a smooth base copper-anode and a plurality of cathode squares plated on a dielectric forming the wall opposite the copper-anode and a laser excitation source which is electrically coupled to the anode and cathode of the structure. The transversely-excited waveguide gas lasers also include an enclosure which encloses the structure and a plurality of gas inlets and outlets which maintain the laser gases at high total gas pressure within the structure. The transversely-excited waveguide gas lasers which have been operated in the quasi-continuous mode at pulse repetition rates as high as 40 kHz, as described in Smith et al., High Repetition-Rate and Quasi-CW Operation of a Waveguide Laser CO.sub.2 TE Laser, Optics Communication, Volume 16, Number 1, January 1976, pages 50-53.
U.S. Pat. No. 4,103,255, entitled High Power, Compact Waveguide Gas Laser, issued Howard R. Schlossberg on July 25, 1978, teaches a high power, compact waveguide gas laser housing located within a resonant cavity. The housing has a longitudinal chamber situated therein. The chamber is divided into a plurality of waveguides by a plurality of infrared transmitting partitions. During operation of the laser, the leakage of laser radiation between adjacent waveguides through the partitions causes coupling of the phases of the waveguide modes thereby producing a laser output of high power.